A quantitative approach to the study of Bancroftian filariasis
Gubler, D.J.; Bhattacharya, N.C.
American Journal of Tropical Medicine and Hygiene 23(6): 1027-1036
1974
ISSN/ISBN: 0002-9637 PMID: 4611252 Document Number: 76946
Exposure to infection with Wuchereria bancrofti was studied for a year in a suburb (Howrah) of Calcutta, India, and correlated with parasitological and clinical observations on the human study population. Blood surveys at the beginning and end of the study showed microfilaraemia rates of 12.4% and 14.8%, respectively. The median microfilarial density remained constant at 18/20 mm3 blood. A clinical survey at the end of the study revealed little severe filarial disease. However, between 30% and 40% of the males in the age-groups above 20 years had milder symptoms suggestive of filariasis, mostly small hydrocoeles and cord abnormalities. Exposure to infection with stage-III larvae was very heavy and continuous throughout the year. It was estimated that a person sleeping indoors during the year of this study would have been bitten by 1850 'infective' examples of Culex pipiens fatigans Wied. carrying a total of 5904 infective larvae. A person sleeping outdoors during the same period would have been bitten by 1352 'infective' females of C. p. fatigans carrying 4056 larvae. This heavy exposure was shown to be primarily due to the extremely high biting density by C. p. fatigans of over 115 000 bites/person annually in the study area. The reasons for the discrepancy between the relatively moderate microfilaremia rates and lack of severe filarial disease, which suggest low exposure to infection, and the epidemiological data, which suggest very high exposure to infection, are discussed.